Par Measurements

I recently rented a PAR meter from my local fish store and spent a day measuring and gathering PAR readings from around my mixed reef tank. I took a lot of measurements. I tried to get a reading for just about every nook and cranny I could fit the PAR meter’s sensor into. I wanted to get a complete picture of how the two 160w Maxspect Razors (R420r)  LED lights hanging over my tank interacted with the rock work so that I could make the best choices possible when placing corals.

OnlyTono 125G PAR MapFor those of you that don’t know, PAR is an abbreviation for Photosynthetically Active Radiation. A PAR meter, or quantum sensor, measures the quantity of usable light as it relates to photosynthesis – generally between the 410-700nm wavelength.  Most corals get the majority of their nutrients for survival through a symbiotic relationship with zooxanthellae bacteria. This specialized bacteria requires light to perform photosynthesis much like a plant does

When it comes to placing corals in a reef tank, great care is required to try and provide the coral the proper amount of light. Too much and you might disrupt or even destroy the zooxanthellae bacteria resulting in bleaching of the coral, too little and it may starve and ultimately waste away.

The Maxspect R420r lights have the ability to ramp up and ramp down over the course of the day. This is achieved by using the light’s built-in controller. The controller provides six time points that can be programed with both a time and intensity. At each point, you can set an intensity level for both the white channel as well as a the blue channel. Below is the lighting program I created for my tank, and the program I used for these PAR measurements.

Custom Maxspect Light Program06:00 – 01 – 00 
07:00 – 50 – 65 
12:00 – 80 – 85 
18:00 – 75 – 90 
18:30 – 50 – 60 
19:00 – 00 – 01


To get the most accurate survey of the PAR levels within my tank, I started by mapping out more than 40 points I wanted measurements from. I chose locations based on current coral placement as well locations I may place corals in the future. I also tried to get a variety of locations with some being in full light, while others either slighting shadowed from the full intensity of light or fully shadowed and at various depths

Since the lights change intensity throughout the day, I also felt it important to take multiple readings for each location for each of the programed time/intensity points. This would also give me the ability to extrapolate the average PAR levels for the entire photo period.

Once I had my map, I began by manually setting the light to the level of the first time period, and began taking measurements. I had Dar (my better half) write down the numbers as I moved around the tank.  Once I was done, I manually set the lights to the intensity of the net time point and continued measuring. I did this until all the locations had been measured at each of the time point intensities.

Next, I dropped these numbers into an Excel doc and extrapolated the values for each measurement so that I would have a number for each hour. I then used these numbers to calculate the average PAR levels across the entire photo period.

In conclusion, I think achieved what I was out to get. I created a very complete map of the PAR levels throughout tank. hopefully this will aid me in making this tank as successful as possible. I also hope you find this information useful for you own tank and particularly for Maxspect R420r owners out there.